1. Field of the Invention
The invention relates to a steering apparatus that detects a zero point of a steering angle of a steering wheel, and a control method thereof.
2. Description of Related Art
In a vehicle behavior control technique such as electronic stability control (available as vehicle stability control (VSC)), various types of control are executed using a detection value from a steering angle sensor attached to a steering wheel. When a type of steering angle sensor that outputs a relative angle is used, a zero point of the steering angle sensor is detected first, and then an absolute steering angle is calculated on the basis of the detected zero point. For this purpose, the steering angle zero point needs to be detected with a high degree of precision. Japanese Patent Application Publication No. 2004-276734 (JP 2004-276734 A), for example, describes a technique of detecting the steering angle zero point on the basis of a difference between an estimated yaw rate estimated from the detection value of the steering angle sensor and an actual yaw rate detected by a yaw rate sensor.
When characteristic variation such as looseness occurs in a steering transmission system from the steering wheel to a vehicle wheel, linearity is no longer maintained between the steering angle and a tire angle, leading to variation in a steering feeling and a reduction in a precision with which vehicle state quantities are estimated based on steering angle information. As a result, precision with which the steering angle zero point is detected may also decrease.